Merge lp:~jtv/maas/clearer-spurious-error into lp:~maas-committers/maas/trunk

[Jeroen T. Vermeulen]

Slightly more helpful detailed message to help diagnose test failures like in bug 1356788.

[Julian Edwards (julian-edwards)]

 review: approve

review: Approve

[Gavin Panella (allenap)]

Your comment from bug 1356788:

  If I make the code go into pdb at the point where it is about to raise
  the exception, and I look into loop.services interactively, I get a
  MultiService object representing an empty list of services. So
  presumably this is a race that will fix itself given time.

was the thing that helped me understand what I'd done wrong. The list of
services was basically irrelevant because RegionEventLoopFixture always
sets up the same set of services.

So, approved because it's fine, but it's actually not particularly
useful information, and for bug 1356788 was a red herring at first.

review: Approve

=== modified file 'src/maasserver/testing/eventloop.py'
--- src/maasserver/testing/eventloop.py	2014-08-12 21:15:25 +0000
+++ src/maasserver/testing/eventloop.py	2014-08-14 09:28:26 +0000
@@ -45,10 +45,13 @@
                 "The event-loop has been left running; this fixture cannot "
                 "make a reasonable decision about what to do next.")
         # Don't proceed if any services are registered.
-        if list(loop.services) != []:
+        services = list(loop.services)
+        if services != []:
             raise RuntimeError(
                 "One or more services are registered; this fixture cannot "
-                "make a reasonable decision about what to do next.")
+                "make a reasonable decision about what to do next.  "
+                "The services are: %s."
+                % ', '.join(service.name for service in services))
 
     def setUp(self):
         super(RegionEventLoopFixture, self).setUp()